Three dimensional integrated circuits (3D IC) offer a host of advantages over traditional circuits: lower power consumption, higher logic density, greater efficiency, alleviating bottlenecks, shorter critical path delays, and lower area cost to name just a few.
3D ICs come in two general forms. In a first configuration, 3D IC chip packages contain two or more integrated circuit dies (ICs) stacked vertically so that they occupy less space. Power and signal communication connections between the vertically stacked ICs can be made using through-semiconductor-vias (TSV), also referred to as through-silicon-vias or through-substrate-vias, which pass through the entire thickness of a die, permitting connections between conductive patterns on the front face and back face of the die.
In a second configuration, a stacked cell 3D IC has a plurality of stacked cells (also referred to as tiers). This configuration is sometimes referred to as monolithic 3D IC or 3D IC vertical structure. In a stacked cell 3D IC, stack components or cells are formed in a vertical above a single semiconductor substrate (as opposed to fabricating individual chips and joining the individual chips together). Components that are traditionally arranged horizontally can be stacked on top of each other to reduce area cost. A stacked cell 3D IC can provide a dense system of vertical interconnectivity by inter-level vias (ILV), also referred to as inter-tier vias, which carry power and communications between the stacked cells.
3D IC packages present many new challenges for designers. One such challenge is heat dissipation. For 3D IC chip packages, if three or more dies are included in the stack, then the interior dies—all of the dies except for the topmost die and bottommost die—are sandwiched between other dies without access to ambient cooling. The same is true for 3D IC stacked cells—all cells except the topmost and bottommost cells lack access to ambient cooling. Effective heat dissipation in the interior dies and interior cells is essential to preventing premature failure of these components.